This invention lies in the field of oil field emulsion treating equipment.
More specifically, this invention lies in the field of electrical emulsion treaters which separate globules of water from oil in a water-in-oil emulsion, by providing AC potentials or pulsed DC potentials between insulated electrodes and the metal surfaces of the treater, to coalesce small droplets to form large ones, which will separate out from the oil.
In the prior art it has long been known that oil field emulsions can be broken or separated by the use of electrostatic fields applied to the emulsion as it flows between a pair of electrodes. The electrical field causes water droplets to be charged and to be attracted to one or the other of the electrodes. In moving toward the electrode, they collide and coalesce with other droplets, to form larger droplets, which by their size then fall in the earth's gravity field, to collect on the bottom of the tank.
It has been found that AC potentials are useful in separating and removing large water droplets in a water-in-oil emulsion. However, for small droplets, a DC potential is preferred. However, in applying a continuous DC potential, it sometimes happens that a continuous string or thread of droplets is formed, which connect between the two electrodes and, therefore, forms a low resistance connection. This can cause damage and burning of the electrodes, and possibly an explosion of the treater tank. Therefore, if DC potentials are used, they must be interrupted in one way or another such as by electrical switching, or by the mechanical separation of electrodes, etc.
It is a primary object of this invention to provide an electrical treater for oil field emulsions, that has a plurality of treating trays with AC potential applied to the electrodes in one or more of the trays, through which the emulsion is first passed, and pulsed DC potentials applied to electrodes in two or more additional trays through which the partially treated oil from the first trays are successively passed.
It is a further object of this invention to provide at least two trays which are supplied separately with pulsed DC potentials in which the pulsed DC potentials are derived from half-wave rectifiers, which rectify alternate half cycles of an AC potential. With pairs of such trays, one tray will carry a rectified potential from one end of the secondary of a transformer, and another tray will carry the rectified output from the opposite end of the secondary of the transformer, with the mid-point of the secondary being grounded to the equipment.